Flying spot scanner blanking

ABSTRACT

A flying spot scanner is employed to inspect a web which rides over a supporting surface. Optical signals are produced at the edges of the web, and at the edges of the surface; and optical web defect signals are produced while scanning the web. To blank signals which are not web dependent, the invention proposes to split scan-produced signals into first and second halves thereof, whereby web-edge defining signals may be isolated, and employed to operate a blanking circuit. To prevent the registering of defects which are proximate the edges of the web, each pair of blank-defining signals produced during a given scan are shifted timewise to a subsequent scan, one of each such pair being shifted a little more, and the other of each such pair being shifted a little less, than a scan duration.

United States Patent Bhullar et a1.

[54] FLYING SPOT SCANNER BLANKING [72] Inventors: Pushpinder S. Bhullar;Robert A. Wright,

both of Rochester, NY.

[73] Assignee: Eastman Kodak Company, Rochester,

[22] Filed: Oct. 19,1970

[21] Appl. No.: 81,969

[ Feb. 29, 1972 Primary Examiner-Ronald L. Wibert AssistantExaminerEdward S. Bauer At!orneyWalter O. Hodsdon and Robert F. Cody[57] ABSTRACT A flying spot scanner is employed to inspect a web whichrides over a supporting surface. Optical signals are produced at theedges of the web, and at the edges of the surface; and optical webdefect signals are produced while scanning the web. To blank signalswhich are not web dependent, the invention proposes to splitscan-produced signals into first and second halves thereof, wherebyweb-edge defining signals may be iso lated, and employed to operate ablanking circuit. To prevent the registering of defects which areproximate the edges of the web, each pair of blank-defining signalsproduced during a given scan are shifted timewise to a subsequent scan,one of each such pair being shifted a little more, and the other of eachsuch pair being shifted a little less, than a scan duration.

6Claims,8Drawing Figures 20 22 24 A DEFECT REG. 7 USING C/(T BLANK CKTQo e1:

'PATENTEDFEBZS I972 3,646,353

SHEET 1 [1F 3 A TTOR/VE VS RT m @E l a? 3 ww all .2 an m ,@\.u 4m J 57WC wv i w w QEQEMQ m m 1 mw Q \A a kwwm m= WW I l AT w Q m R i .2 4 0 EBM Ex q m J WK mEPfiwQ w Q x a 396 Q Q 5% b9 @E J 5}: Q q u x w .9 m Wwm9 mt mw/ 55 m q Q 11 355m H N y .WQQIQ Q Tl l PATENTEUFEB29 m2 SHEET 2OF 3 A TTORNEYS FLYING SPOT SCANNER BLANKING BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates in general toflying spot scanners, and in particular to such scanners as are usefulfor inspecting webs and the like.

2. Description Relative to the Prior Art Consider a web which, whilebeing subject to the spot of a flying spot scanner, passes over a wideweb-supporting surface. Modulation of the spot occurs as the spot (1)first passes onto the web-supporting surface, (2) passes from suchsurface onto the edge of the web, (3) passes over defects in the web,(4) passes from the edge of the web back onto the web-supportingsurface, and (5) moves off the web-supporting surface. Generally, onlyspot modulation caused by web defects is useful for determining webquality; and thus, it is the prior art practice to blank, by one meansor another, spot modulation which is not defect-dependent.

It frequently obtains that web defects are created, near the edges of aweb, as a result of slitting, and otherwise handling, the web; and thus,blanking must also cancel edge-defect modulation to prevent inadvertentregistration of defects which have no material bearing on the quality ofthe web.

US. Pat. No. 3,198,951, indicates a blanking method which is dependenton placing photopickups proximate the edges of a web, respectively toturn-on and turnoff a defect detection circuit.

US. Pat. Nos. 3,360,651 and 3,510,664, both, apparently, recognize thatthe system of US. Pat. No. 3,198,951 (1) cannot tolerate weaving of aweb over a supporting surface, (2) requires repositioning ofphotopickups to accommodate different size webs, and (3) cannot beeffective, without modification, for inspecting webs of nonuniformwidth. U.S. Pat. Nos. 3,360,651, and 3,510,664, suggest that spotmodulation, as caused by web edges, be used for blanking purposes: theformer producing a gate-on pedestal pulse in response to the lead edgeof a web; and the latter employing a counting technique for gating onand off, and registering defects.

US. Pat. No. 3,360,651, is considered closest, in concept, to thepresent invention: U.S. Pat. No. 3,360,651, teaches that spot modulationcorresponding to the edges of the web may be used to define a pedestalpulse for gating a defect detector into and out of operation. Inaddition, US. Pat. No. 3,360,651, teaches the effective narrowing ofsuch pedestal pulse to prevent defect detection at the edges of the webunder inspection. Pedestal narrowing is accomplished in US. Pat. No.3,370,651, by pulse delay techniques involving feedback controls; andwhereby the system of US. Pat. No. 3,360,651, automatically corrects forwebs of varying widths.

So long as the surface over which the web of U.S. Pat. No. 3,360,651,passes is unproductive of signals as the flying spot of the scanner inquestion moves onto and OK such surface, the system of US. Pat. No.3,360,651 will undoubtedly be effective for its intended purpose.Consider, however, the production of scan signals having theabove-mentioned five occurrences of modulation during a given scan.Needless to say, were signals of such type to be applied to the Schmitttrigger circuit of US. Pat. No. 3,360,651, such circuit wouldundesirably operate two extra times during each scan of the flying spot,thereby preventing the proper operation of its pedestal definingcircuit. Such extra triggering occurs because scan signals, of the typeto be handled by apparatus according to the invention, produces twopositive and two negative spike pulses for each flying spot scan,whereas scan signals which are handled by the apparatus of US. Pat. No.3,360,651, produce only two spike pulses for each flying spot scan.

SUMMARY OF THE INVENTION The invention principally concerns a way todistinguish between pulses which define the edges of a web, as opposedto pulses which define the edges of a web-supporting surface.

Distinguishing between such pulses, according to the invention, ispredicated on the use of clock pulses: A first clock pulse correspondingto a first portion (half) of the scan signal gates signals of one senseto an edge blank circuit (or pedestal producing circuit); and a secondclock pulse corresponding to a second portion (half) of the scan signalgates signals of the opposite sense to the edge blank circuit (orpedestal producing circuit). In one version of the invention, each scansignal has, during each of its halves, first and second pairs of steeppositiveand negative-going signal changes. By using a first clock togate the positive-going signal change of the first scan signal half, andby using a second clock to gate the negativegoing signal change of thesecond scan signal half, the inner and outer bounds of the web may bedefined. In other words, the present invention proposes to split thescan signal into halves, by means of the aforesaid clock pulsetechnique, thereby to distinguish the pulses which define the bounds ofthe web-supporting surface, and of the web itself.

Two other aspects of the invention obtain: (1) a technique for producinga pulse that appears to occur in response to, but before another pulse,and (2) a technique for distinguishing between large defect signalsduring a flying spot scan, and signals which result from spot modulationcaused by the websupporting surface.

OBJECTS OF THE INVENTION 1. To provide blanking in a flying spot scannersystem employed to inspect webs that are supported on a signal-producingsurface;

2. To simulate the generation of a pulse a predetermined time before theoccurrence of a signal which appears to trigger such pulse, etc.

The invention will be,described with reference to the V figures,wherein:

FIG. 1 illustrates in block form a web inspection system adapted toaccommodate the invention,

FIG. 2 illustrates a signal form of a type which may be processed bymeans of the invention,

FIG. 3 is a schematic block diagram of a circuit according to theinvention,

FIG. 4 is a plan view of a web illustrating scan dimensions according tothe invention in a presently preferred form thereof,

FIG. 5 is a block diagram of a circuit which may be connected into thecircuit of FIG. 3 to provide the scan dimensions indicated in FIG. 4,

FIG. 6 illustrates pulse diagrams useful for describing the combinedapparatuses of FIGS. 1, 3, and 5,

FIG. 7 is an overall block diagram of apparatus embodying the variousfeatures of the invention, and

FIG. 8 illustrates pulse diagrams useful for understanding the operationof the circuit of FIG. 7.

Referring to FIG. 1, a flying spot scanner 10 causes a beam of radiationto sweep across a web 12 which rides over a websupporting roller 14. Theroller 14 has a reflectivity different from that of the web 12; andlight reflected from the web 12 and roller 14 is collected by optics l6and directed to a photodetector 18. Each flying spot scan produces anoptical signal like that shown in FIG. 2.

FIG. 2 indicates that the optical signal applied to the photodetector 18increases (C) as the flying spot first goes onto the (shiny) surface ofthe roller 14, drops (D) as the spot goes onto the web 12, varies inresponse to web defects, increases (A) when the spot goes back onto the(shiny) roller, and drops (B) to an ambient level when the spot goes offsuch roller.

Output signals from the photodetector 18 are amplified (20) and appliedto a gate circuit 22 which, in turn, applies such signals to a device 24for registering the occurrence of defect representative signals.Operation of the gate circuit 22 depends on the occurrence of an edgeblank pulse from a circuit 26, which pulse inhibits the operation of thegate circuit 22. The edge blank circuit 26 receives the amplifier 20output signals, and signals from a photodetector 28 (and amplifier 30)that defines the point at which the flying spot first starts to sweepacross the roller-and-web, thereby to produce the edge blank pulses. Thephotodetector 28 output signals have a scan duration (ST) as indicated.

The edge blank circuit 26 of FIG. 1 is indicated in detail in FIG. 3;note contacts P,Q,R:

A differentiator circuit 32 is adapted to receive the flying spot scansignal (FIG. 2); and produces therefrom a pair of spike pulsescorresponding to the signal changes C,D and A,B. Since the signalduration which occurs between D and A corresponds to the period ofscanning which is of interest, the invention proposes to isolate thesignal occurrences D and A, each by means of a respective clock pulse.Such isolation is necessary because of the signal producingcharacteristics of the web-supporting roller 14 which is to say thatpositiveand negative-going spike pulses are produced during both thefirst and second halves of each scan (ST). The negative-going signal (D)that defines the lead edge of the web is isolated from thenegative-going signal (B) that defines the trailing edge of theweb-supporting roller 14 by means of a polarity detector 33 and a clockfrom afirst half-cycle detector 34, and the positive-going signal thatdefines the trailing edge (A) of the web 12 is isolated from thepositive-going signal (C) that defines the lead edge of theweb-supporting roller 14 by means of a polarity detector 35 and a clockfrom a second half-cycle detector 36. The half-cycle detectors 34,36 maytake the form of counter leads on a monostable multivibrator that isresponsive to the output of the roller-edge defining photodetector 28;such a multivibrator having a cycle of operation corresponding to theduration ST/2.

A pair of AND-gates 40,42 respectively receive the negativeandpositive-going spike pulses, and the first and second half cycle clocks;and attendantly, such AND-gates 40,42 respectively produce the web-scandefining pulses D and A which turn a flip-flop 44 off and on, therebyrespectively to uninhibit and inhibit the operation of the gate 22. Thecrosshatched area of the signal output of the flip-flop 44 represents anedge blank pulse so produced.

As stated above, it frequently obtains that a web is to be inspectedacross less than its full width (see dimensions Z-X, FIG. 4), thereby toprevent the ragged edges 46 of the web from producing defect signals.This means the blank pulse must be widened; which at first blushsuggests that the edges A and D of the flip-flop 44 output are to berespectively advanced and delayed. However, since the occurrence of suchedges are unpredictable, i.e., they depend on the nature of the scansignal, the matter of edge advancing, as opposed to edge delaying, is animpossibility. To simulate edge-advancing, the invention proposes asignal delay technique: the signal (A) to be advanced being delayed fora little less than the duration ST; and the signal (D) to be delayedbeing delayed a little longer than the duration ST. Thus, in accordancewith the invention, signals which are produced during one scan areemployed for generating a widened blanking pulse for use during asubsequent scan. FIG. 5 shows a circuit adapted to be connected tocontacts L,M,R of FIG. 3 to implement the widening of an edge blankpulse, i.e., the circuit of FIG. 5 indicates appropriate delay devices48,50 cooperative with the flip-flop 44 Reference should now be had toFIG. 6 which graphically illustrates how blank-defining pulses A, and D,effect a blanking pulse that overlaps (by At and At) blank-definingpulses A and D which is to say that blanking, for a given flying spotscan, is determined during an earlier scan and such blanking will beeffective for ordinary rates of web travel.

The following description, relating to apparatus of FIG. 7, indicates aworking arrangement for the circuit techniques discussed above inconnection with FIGS. 3 and 5: Similar characteristic notations areemployed in all such figures for corresponding components. See also thewaveforms of FIG. 8:

A monostable multivibrator, responsive to the output of thephotodetector 28, produces a pair of complementary clock pulses (34,36),each having a duration ST/2. For polarity detectors 33,35, Schmitttriggers respectively responsive to predetermined negative and positivesignal level outputs from the differentiator 32 are employed; and theirrespective outputs are applied to the AND-gates 40,42 together withrespective clocks 34,36, thereby to isolate the signals D and A.

To delay the signal D, as required, a pair of multivibrators 48, and 48,are employed. The multivibrator 48, produces a pulse of duration ST/Z;and the multivibrator 48 responsive to the trailing edge of the pulsefrom the multivibrator 48,, produces a pulse of duration ST/2+At.

Similarly, the signal A is delayed by a pair of multivibrators S0, and50 the former for a duration ST/2, and the latter for a duration ofST/2-At.

By means of the D and A delays 48,50, the flip-flop 44 (bistablemultivibrator) is respectively reset and set-in response to a given pairof D and A signals-a little more, and a little less, than a scanduration after such D and A signals are produced, thereby causing themultivibrator 44 to appear to reset in response to, and after, a signalwhich has just occurred, and to set in response to, and before, a signalwhich has not yet occurred.

The bistable multivibrator 44 serves to inhibit the gate 22 in themanner described above.

For certain web defects, such, for example, as a break or hole in theweb being inspected, steep large amplitude signals S, sufficient totrigger the (positive) Schmitt trigger 33, are applied to thedifferentiator 32. See scan 3, FIG. 8. When a signal S occurs during thesecond half of a flying spot scan, it is gated through the AND-gate 42and will, absent the improvement to be described presently, effectivelywiden the blanking pulse so that the defect S will go undetected. (Thesecond half of a flying spot scan, as opposed to the first half, is ofconcern for the reason that only during the second scan half arepositive thresholds of interest.) To avoid so widening the blankingpulse, in response to a large defect signal, that such signal may goundetected, the invention proposes to change circuit timing in responseto large defect signals S, so that the signal A will turn off theflip-flop 44 (i.e., so inhibit its operation that it remains in itsreset state), thereby to cause defect registration (24) to be inresponse to signal outputs produced from the web-supporting roller 14.

To this end, an AND-gate 60 is adapted to receive the signal A and thedelayed half cycle pulse of the multivibrator 50, and, since suchsignals are usually of opposite polarity, the AND-gate 60 usually has nooutput. As soon, however, as the multivibrator 50, has the timing of itsoutput pulse shifted by a signal S, the signal A gets gated out of theAND-circuit 60. A multivibrator 62, the purpose of which is tocomplement the half-cycle delay of the multivibrator 50, so that theeffect of the isolated signal A will be a full scan duration after itsoccurrence, sets a bistable multivibrator 64 so that such multivibratormay inhibit the operation of the blank pulse producing multivibrator 44.Thus, the occurrence of a large defect signal S during the second halfof a scan duration effectively turns off the multivibrator blanker 44,the gate circuit 22 being thereby left open so that signals from theweb-supporting roller may be registered.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention. For example, whereas half-cycle clocks are indicated, suchclocks may be longer or shorter durationwise than a half-cycle, so longas they complement occurrencewise the pulses which they are intended toisolate; the durations At and At may be alike or different; the delaysafforded by the components 48,50 may be respectively a little more and alittle less than multiples of the duration ST, etc.

What is claimed is:

l. A system for inspecting webs which are conveyed over a means of theoutput of said first AND gate means by a duweb-supporting surface, saidsurface and said web having subration slightly longer than a givenmultiple of the time stantially different abilities to modulate incidentradiation, that it takes to sweep radiation across said surface andcomprising: said web, and

a. a flying spot scanner for beaming and sweeping, at a given 5 b.second means for delaying the application to said bistable cyclic rate,a source of radiation across said surface and means of the p t f aid end AND gate means by a said web, duration slightly less than said giventime multiple.

b. means for collecting radiation from said surface and said Theapparatus of Claim 21 b f producing i l corresponding to respective a.wherein said first delay means comprises first and second di ti sweeps,l0 monostable multivibrators for producing respective c. gate circuitmeans adapted to receive signals produced by Square Wave Signals, firstmultivibrator being p Said radiation collecting means, and sive to theoutput of said first ANl) gate means and said means f producing gatingsignals for controlling the second multivibrator being responsiveto thetrailing edge operation of said gate circuit means, said means for f theoutput 9 sald first multfvlbratorj the producing gating Signalscomprising: bined durations of sa d square wave signals beingslightly 1. means for producing first and second sets of clock greaterthan the Sam Sweep of Sam flymg Spot signals, the signals of said firstset corresponding durationwise with the first half of each saidradiation sweep, wherem second i means compnses. thud and and thesignals of said second set corresponding durafijurth monostable.mumvlbrinors. for profhfcmg i tionwise with the Second half of eachSaid radiation two square wave signals, said third multivibrator beingSweep responsive to the output of 531d second AND gate means 2 f d ti til and said fourth multivibrator being responsive to the trailmeans orrecelymg l 3 Sal S'gna S ing edge of the signal output of said thirdmultivibrator, producfzd Sald radlanon. collefmng means the combineddurations of said square wave signals from pmducmg pans of edge'ckfimngSplke P l dunng said third and fourth multivibrators being slightly lessthe first and second halves of each radiation sweep, than the Said Sweeptime ofsaid flying Spot seamen said spike pulsescorresponding toradiation modula- 4 The apparatus ofclaim 1 including: non Sald radlanonsweeps onto and Off Sald a. circuit means for distinguishing betweensaid edge definporting surface, ing spike pulses and spike pulsesproduced in response to 3. first and second AND gate means for receivingrespeclarge web defects and tively said first and second sets of clocksignals, b. means responsive to defect-produced spike pulses for 4.means for applying the spike pulses, corresponding to placing said gatecircuit means in its signal passing state.

radiation modulation as said radiation sweeps from said h apparatus OfClaim 1 wherein: Surface onto said Web, to said first AND gate means, a.said web has a photographically sensitized surface, 5. means forapplying th spike l corresponding to b. said web-supporting surface is aroller drum, the axial radiation modulation as said radiation sweepsfrom said dimension of which is Wide! than Said and b onto id Surface,to id Second AND gate means, c. said roller drum, at least proximate itsextremities, has a d mirrorlike surface. 6. bistable means cooperativewith said gate circuit apparatus of f h 5 iflcludingi means, andresponsive to the pulse outputs of both said 40 F l means fordlstlllgulshmg bfitwee" l g AND gate means, thereby to place said gatecircuit "8 spike Pulses and Spike Pulses Preduced response to means in asignal pasing state while said radiation large web defecisi and Sweepsacross Said web b. means responsive to defect-produced spike pulses forThe apparatus ofclaim 1 including: AND gate placing said gate circuitmeans in its signal passing state. a. first means for delaying theapplication to said bistable

1. A system for inspecting webs which are conveyed over a websupportingsurface, said surface and said web having substantially differentabilities to modulate incident radiation, comprising: a. a flying spotscanner for beaming and sweeping, at a given cyclic rate, a source ofradiation across said surface and said web, b. means for collectingradiation from said surface and said web for producing signalscorresponding to respective radiation sweeps, c. gate circuit meansadapted to receive signals produced by said radiation collecting means,and d. means for producing gating signals for controlling the operationof said gate circuit means, said means for producing gating signalscomprising:
 1. means for producing first and second sets of clocksignals, the signals of said first set corresponding durationwise withthe first half of each said radiation sweep, and the signals of saidsecond set corresponding durationwise with the second half of each saidradiation sweep,
 2. means for receiving and differentiating said signalsproduced by said radiation collecting means for producing pairs ofedge-defining spike pulses during the first and second halves of eachradiation sweep, said spike pulses corresponding to radiation modulationas said radiation sweeps onto and off said web-supporting surface, 3.first and second AND gate means for receiving respectively said firstand second sets of clock signals,
 4. means for applying the spikepulses, corresponding to radiation modulation as said radiation sweepsfrom said surface onto said web, to said first AND gate means,
 5. meansfor applying the spike pulses, corresponding to radiation modulation assaid radiation sweeps from said web onto said surface, to said secondAND gate means, and
 6. biStable means cooperative with said gate circuitmeans, and responsive to the pulse outputs of both said AND gate means,thereby to place said gate circuit means in a signal passing state whilesaid radiation sweeps across said web.
 2. means for receiving anddifferentiating said signals produced by said radiation collecting meansfor producing pairs of edge-defining spike pulses during the first andsecond halves of each radiation sweep, said spike pulses correspondingto radiation modulation as said radiation sweeps onto and off saidweb-supporting surface,
 2. The apparatus of claim 1 including: AND gatea. first means for delaying the application to said bistable means ofthe output of said first AND gate means by a duration slightly longerthan a given multiple of the time that it takes to sweep radiationacross said surface and said web, and b. second means for delaying theapplication to said bistable means of the output of said second AND gatemeans by a duration slightly less than said given time multiple.
 3. Theapparatus of claim 2: a. wherein said first delay means comprises firstand second monostable multivibrators for producing respective squarewave signals, said first multivibrator being responsive to the output ofsaid first AND gate means and said second multivibrator being responsiveto the trailing edge of the signal output of said first multivibrator,the combined durations of said square wave signals being slightlygreater than the said sweep time of said flying spot scanner, and b.wherein said second delay means comprises third and fourth monostablemultivibrators for producing respective square wave signals, said thirdmultivibrator being responsive to the output of said second AND gatemeans and said fourth multivibrator being responsive to the trailingedge of the signal output of said third multivibrator, the combineddurations of said square wave signals from said third and fourthmultivibrators being slightly less than the said sweep time of saidflying spot scanner.
 3. first and second AND gate means for receivingrespectively said first and second sets of clock signals,
 4. means forapplying the spike pulses, corresponding to radiation modulation as saidradiation sweeps from said surface onto said web, to said first AND gatemeans,
 4. The apparatus of claim 1 including: a. circuit means fordistinguishing between said edge defining spike pulses and spike pulsesproduced in response to large web defects, and b. means responsive todefect-produced spike pulses for placing said gate circuit means in itssignal passing state.
 5. The apparatus of claim 1 wherein: a. said webhas a photographically sensitized surface, b. said web-supportingsurface is a roller drum, the axial dimension of which is wider thansaid web, and c. said roller drum, at least proximate its extremities,has a mirrorlike surface.
 5. means for applying the spike pulses,corresponding to radiation modulation as said radiation sweeps from saidweb onto said surface, to said second AND gate means, and
 6. biStablemeans cooperative with said gate circuit means, and responsive to thepulse outputs of both said AND gate means, thereby to place said gatecircuit means in a signal passing state while said radiation sweepsacross said web.
 6. The apparatus of claim 5 including: a. circuit meansfor distinguishing between said edge-defining spike pulses and spikepulses produced in response to large web defects, and b. meansresponsive to defect-produced spike pulses for placing said gate circuitmeans in its signal passing state.